Shape-changing structure member with embedded spring

ABSTRACT

A shape-changing structural member has a shape-changing material, such as a suitable foam material, for example a polymer foam capable of withstanding at least 300% strain or a metal alloy foam capable of withstanding at least 5% strain. Springs, such as one or more coil springs, provide structural support for the shape-changing material. The springs may also be used to provide forces to expand and contract the shape change material. The springs may include pairs of concentric springs, one inside of another. The concentric springs may surround an underlying skeleton structure that supports the shape-changing material and/or aids in changing the shape of the material. The concentric springs may or may not be wrapped around the underlying skeleton structure. Multiple springs or pairs of springs may be coupled together using a sheet metal connector.

RELATED APPLICATIONS

This application is related to two commonly-assigned concurrently-filedapplications, “Structure with Reconfigurable Polymer Material” (AttorneyDocket No. PD-06W163), and “Shape-Changing Structure with SuperelasticFoam Material” (Attorney Docket No. PD-07W090). Both of theseapplications are hereby incorporated herein by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The invention is in the field of reconfigurable structural members.

2. Description of the Related Art

Metal foam materials have been used in static structures, such as forbone replacement.

Shape memory polymer materials have been used for morphing or shapechanging structures, components, and hardware. Unlike shape memoryalloys, shape memory polymers do not exert enough force during shapechange to overcome anything but the weakest of forces. Attempts havebeen made to develop structural supports to prevent the shape memorypolymer material from warping out of desired shapes. However, this hasbeen found to severely limit the shape changes that practically can beachieved.

It will be appreciated that there is room for improvement in the area ofuse of shape memory polymer materials.

SUMMARY OF THE INVENTION

According to an aspect of the invention, a shape-changing structuremember includes a shape-changing material supported coil springs withinthe material.

According to another aspect of the invention, a shape-changingstructural member includes: a shape-changing structural material capableof elastic deformation at strains of at least 5%; and one or moresprings embedded in the shape-changing structural material, wherein theone or more springs provide structural support to the shape-changingmaterial.

According to yet another aspect of the invention, an extendible aircraftwing includes: a shape-changing material configured to be extended andretracted; and a pair of concentric springs embedded in theshape-changing material. The springs have an axial length in a directionin which the shape-changing material is to be extended and retracted.The springs provide structural support to the shape-changing material.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims. The following description and the annexeddrawings set forth in detail certain illustrative embodiments of theinvention. These embodiments are indicative, however, of but a few ofthe various ways in which the principles of the invention may beemployed. Other objects, advantages and novel features of the inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings, which are not necessarily to scale:

FIG. 1 is an oblique view of one structural member in accordance with anembodiment of the present invention, an extendable wing, with the wingillustrated in the retracted configuration;

FIG. 2 shows the wing of FIG. 1 in an extended configuration;

FIG. 3 shows the wing of FIG. 1 with the shape-changing material removedto show underlying extendable skeleton;

FIG. 4 shows the wing of FIG. 1 in an extended configuration, with theshape-changing material removed to show the underlying extendableskeleton segments;

FIG. 5 is a cross-sectional view showing one spring configuration foruse in the wing of FIG. 1;

FIG. 6 is an oblique view showing part of the spring configuration ofFIG. 5;

FIG. 7 is a diagram showing a possible the functional relationship ofparts of a structural member in accordance with an embodiment of theinvention;

FIG. 8 is a cross-sectional view showing a second spring configurationfor use in the wing of FIG. 1; and

FIG. 9 is a cross-sectional view showing a second spring configurationfor use in the wing of FIG. 1.

DETAILED DESCRIPTION

A shape-changing structural member has a shape-changing material, suchas a suitable foam material, for example a polymer foam capable ofwithstanding at least 300% strain or a metal alloy foam capable ofwithstanding at least 5% strain. Springs, such as one or more coilsprings, provide structural support for the shape-changing material. Thesprings may also be used to provide forces to expand and contract theshape change material. The springs may include pairs of concentricsprings, one inside of another. The concentric springs may surround anunderlying skeleton structure that supports the shape-changing materialand/or aids in changing the shape of the material. The concentricsprings may or may not be wrapped around the underlying skeletonstructure. Multiple springs or pairs of springs may be coupled togetherusing a sheet metal connector, such as a piece of straight or curvedsteel.

FIGS. 1 and 2 show two configurations of a one example of ashape-chancing structure, a wing 10 that has a variable wingspan. Thewing 10 has a number of shape-changing members 12, here being portionsof the wing 10. The shape-changing wing members 12 can be expanded andcontracted to change their shapes. FIG. 1 shows the wing 10 in a first(extended) configuration, with the segments 12 each increased in volume,and lengthened in the direction of the wingspan. FIG. 2 shows the wing10 in a second (retracted) configuration, with the members 12 having areduced extent in the direction of the wingspan.

The members 12 each have a shape-changing material 14. A shape-changingmaterial is defined herein as a material capable of elastic deformationat strains of at least 5%. Certain types of shape-changing material,such as polymer foams, may be capable of elastic deformation at muchlarger strains, such as at strains of 300% or 400%. The shape-changingmaterial 14 may be a foam material able to expand and contract in one ormore directions, changing the volume of the material. The shape-changingmaterial 14 may also be a solid material, which as used herein refers toa material that is substantially without voids.

The shape-changing material 14 may be a shape memory polymer material,either in solid form, as a foam, and/or as a gel. As explained ingreater detail below, the polymer material may have mixed in itparticles that are acted upon by the electromagnetic field.

Alternatively the shape-changing material may be a superelastic metalfoam material 14. Superelasticity, sometimes referred to aspseudoelasticity, refers to a situation where a solid material undergoesa phase transformation that causes a reduction of the material's modulusof elasticity (Young's modulus). When mechanically loaded, asuperelastic material may reversibly deform to very high strains, suchas strains of 5 to 10%, or (more narrowly) strains in the range of 6 to8%. The superelastic foam material may be a suitable metal alloy foam.One example of a suitable metal alloy for producing a superelastic metalfoam material is a nickel titanium alloy, such as nitinol. The nitinolmay be 55% nickel by weight, although other proportions may be used.Other possibilities include alloys of copper and zinc, with or withoutaluminum. In addition, the material for the superelastic foamalternatively be a suitable metallic glass. The superelastic metal foamof the members 12 may have a density as low as 10 to 20 percent of thetheoretical density, when the foam is in an expanded state. It will beappreciated that other suitable foam densities may be employed.

The shape-changing members 12 have continuous outer surfaces 16 thatremain continuous and unbroken throughout the shape change process. Theshape changing process of the structure 10 thus is distinguished fromstructural movements in which one discrete part moves as a wholerelative to another part. The maintenance of a continuous outer surfaceduring a shape change process is advantageous in a wing, since acontinuous outer surface may provide better aerodynamic properties forthe wing. Shape change while maintaining a continuous outer surface maybe referred to herein as “morphing.”

FIGS. 3 and 4 show a skeleton 30 of the structure 10. The skeleton 30includes one or more rigid members that underlie or otherwise supportthe shape-changing material 14. The skeleton 30 may be made of asuitable rigid material, such as a suitable metal. The skeleton 30 mayitself be able to change shape, for example by being provided with anactuator to allow it to change its length, or by having parts sliderelative to each other. Such actuation may be done with any of a varietyof forces, such as by use of hydraulics, electrical motors, orpiezoelectric materials. It will be appreciated that providing acontinuous surface is desirable in a large number of situations, forexample in reducing drag of aircraft and other moving vehicles. Theskeleton 30 may provide support for the shape-changing material 14,and/or may be used to provide the force for putting a strain on theshape-changing material 14, to change the shape of the shape-changingmaterial 14 when the material is in a “soft” state.

The various members in the structure 10 may be expanded/retractedindividually, or substantially simultaneously. The shape-changingmembers 12 may be separated into segments that may be individuallyextended and retracted. The segments may be bordered by ribs 32 (FIGS. 1and 2) which may provide structural support, as well as serving aselectrically conductive plates for heating and/or providingelectromagnetic forces. The change in wing length may be performed tooptimize speed-related characteristics of an aircraft. Longer wings maybe more suitable for long-duration low-speed flying, while shorter wingsmay be more suitable for faster speeds.

In addition to the skeleton 30, the shape-changing material 14 may besupported or reinforced by one or more coil springs embedded within thematerial 14. In addition, the springs may aid in providing the force toextend or retract the material 14. More generally, the springs mayfacilitate changing the shape of the shape-changing material. Severalpossible spring configurations are described below.

FIGS. 5 and 6 shows a pair of concentric coil springs 40 and 42 thatsurround and enclose the skeleton 30. The springs 40 and 42 have anaxial (longitudinal) length in a direction along with the shape-changingmaterial 14 is to be extended and retracted (along the direction ofextension/retraction of the skeleton 30). The springs 40 and 42 providestructural support to the shape-changing material 14 that the springs 40and 42 are embedded in. It will be appreciated that the springs 40 and42 may be configured to elastically expand and contract (change theirlengths) by a large amount. The springs 40 and 42 may be capable of anelastic length extension by a factor of 4 or 5. The springs 40 and 42are anchored to structural material on opposite sides of theshape-changing material 14, such as the ribs 32 (FIG. 1).

One or both of the springs 40 and 42 may be made of a shape memoryalloy, which may be solid or a metal foam. One type of shape memoryfeature involves the material changing crystalline structure, in essencechanging phase, at certain temperatures when the material is heated andcooled. This allows the material to “learn” a certain shape that may beregained by subsequent heating, after cooling and shape change of thematerial. Other shape memory materials rely on other forces, such asmagnetic forces, to trigger the shape memory feature. Shape memoryfeatures rely on transitions between various crystal structures that thematerial can be in. For example, the material may transition betweenaustenite and martensite at certain temperatures while being heated andcooled. The material shape is set by heating the material well into thehigh-temperature austenite phase, and holding the material in place.Subsequently cooling of the material causes a transition into thelow-temperature martensite phase. The material can be freely deformed inthe martensite phase. Then when the material is subsequently heated sothat it transitions to the austenite phase, the material spontaneouslyreverts to the shape set into it previously when it was at a hightemperature in the austenite phase.

In addition, the metal alloy material of the springs 40 and/or 42 maytransition from a high-modulus “strengthened” (“stiff” or “hard”) stateto a low-modulus “relaxed” or (relatively) “soft” state as the materialpasses through a transition temperature. For a metal alloy thistransition temperature may correspond to a temperature at which atransition or phase transformation in the metal alloy occurs. Thetransition temperature at which the phase transformation takes place canbe manipulated by how the metal material is alloyed or otherwise formed,and by how the metal material has been heat treated. The transitiontemperature thus may be set at a chosen temperature above a temperatureof the environment around the foam material. Alternatively, thetransition temperature may be set below a normal operating temperatureof the material, or the environment around the material.

Where both of the springs 40 and 42 are made of shape memory alloys, thesprings 40 and 42 may be set to have different transition temperatures,for example by having different compositions of the alloys of the twosprings 40 and 42. The use of shape memory alloys having differenttransition temperatures allows the springs 40 and 42 to act as abi-directional actuator for extending and retracting the shape-changingmaterial 14 of the shape-changing member 12. Changing the temperature ofthe springs 40 and 42 individually changes the modulus of elasticity(Young's modulus) of the springs 40 and 42. In addition, heating may beused to cause the shape memory feature of the springs 40 and 42 toselectively separate or bring together plates, such as the ribs 32(FIGS. 1 and 2), that are on opposite sides of the shape-changingmaterial 14.

The springs 40 and 42 may act as a bi-directional actuator even if onlyone of the springs 40 and 42 is made of a shape memory metal alloy. Thespring made of a conventional material, such as steel, will notsignificantly change its stiffness over a range of operatingtemperature. The spring made of a shape memory alloy will significantlychange its stiffness as it passes through the transition temperature.The shape memory alloy material spring may be configured to have amodulus of elasticity above that of the conventional material springwhen the shape memory alloy is in its stiff or hard state, below thetransition temperature. The shape memory alloy material spring also maybe configured to have a modulus of elasticity below that of theconventional material spring when the shape memory alloy is in its softstate, above the transition temperature. Thus the shape memory alloyspring may be dominant in shaping the material 14 below the transitiontemperature, and the conventional material spring may be dominant abovethe transition temperature.

The shape memory alloy for the springs 40 and/or 42 may be any of avariety of known shape memory materials. An example of a suitablematerial is nitinol. The metal alloy of the springs 40 and/or 42 may bethe same as or different from the metal alloy (if any) in theshape-changing material 14.

It will be appreciated that as another alternative both of the springs40 and 42 may be made of conventional material. In such a situation thesprings 40 and 42 provide structural support only, and are not used toactuate extension or retraction of the material 14. For this alternativethe springs 40 and 42 may be replaced by a single coil spring.

One or both of the springs 40 and 42 may be used for electricallyheating the surrounding shape-changing material 14. The heating may beused to soften the material 14, for example bringing the material 14above a glass transition temperature or a phase transition temperature.The electrical heating may also be used for bringing a shape memoryalloy of the heated spring(s) above a transition temperature.

The springs 40 and 42 may extend across one or more discrete segments ofthe shape-changing material 14. As mentioned above, the springs 40 and42 may be attached to structural members, such as the ribs 40 and 42,bordering or within the shape-changing material 14.

With reference now to FIG. 7, the shape-changing material 14 may be asolid or foam shape memory polymer material 52. As is known, shapememory polymer materials and other materials may be heated above a glasstransition temperature or plastic temperature, to enable them to changetheir shapes. However, when doing so it may be desirable to have theshape memory polymer material 52 still able to resist some forces on it.This ability to resist loads is greatly reduced when the shape memorypolymer material 52 is sufficiently heated so as to soften it to allowit to change shape. For example, during shape change the Young's modulusof shape memory polymer foam is relatively low, and therefore thepolymer material may not be able to carry significant loads. Somemechanism may be needed to increase the stiffness of the material whenit is in this condition, in order to have the material resist loads. Thesprings 40 and 42 (FIG. 5) provide one such mechanism.

In addition, a shape-controlling electromagnetic field system 58 may beused to aid in maintaining the shape of the polymer material 52. Theelectromagnetic field system 58 includes an electromagnetic source 60and a pair of electromagnetic elements 62 and 64. As shown in FIG. 7,the electromagnetic elements 62 and 64 may be on opposite sides of theshape memory polymer material 52. It will be appreciated that a widevariety of number, size, and configuration of electromagnetic elementsare possible. For example, the electromagnetic elements 62 and 64 may beplates or wires. As another example the electrical elements may be metalfoil elements embedded in the polymer material 52. It will beappreciated that the electromagnetic elements may be located in any of avariety of places within or near the material 52.

The electromagnetic field system 58 may provide an electric field and/ora magnetic field for controlling shape of the shape memory polymermaterial 52. Thus the electromagnetic elements 62 and 64 may beelectrical elements, such as capacitor plates. Alternatively, theelectromagnetic elements 62 and 64 may be magnetic field elements, suchas coils.

The electromagnetic elements 62 and 64 may act on an inherent propertyof the shape memory polymer material 52. For instance, theelectromagnetic field system may set up an electric field that acts on adielectric constant of the shape memory polymer material 52.

The shape memory polymer material 52 may have particles 66 interspersedwithin it that are acted upon by the electromagnetic field system 58.The particles 66 may be magnetic particles that receive a force whenacted upon by magnetic field set up by the electromagnetic field system58. The magnetic particles may be magnetite particles. Particles thatrespond to an electrical field may be piezoelectric material particles.Additives to the shape memory polymer material 52 to increase itsdielectric constant may include titanates or titanium compounds. Anysort of suitable particles with a high dielectric constant would beuseful for this purpose. The particles 66 may be micron-size tonano-size particles.

The electromagnetic field system 58 may be used to heat the shape memorypolymer material 52 in order to soften the material to change its shape.Alternatively or in addition one or more separate heating elements 68may be used to heat the shape memory polymer material 52. As discussedabove, the springs 40 and 42 (FIG. 5) may be used as separate resistiveheating elements.

It will be appreciated that a wide variety of suitable additives may beused to make a polymer a shape memory polymer. The glass transitiontemperature and other characteristics of the shape memory polymermaterial may be controlled by the type and amount of additives. Othercharacteristics for the shape memory polymer material may be suitabilityfor the chemical or other environment that the material is exposed to.The shape memory polymer material 52 may be either a polyurethane-basedmaterial or an epoxy-based material. Cyanate-ester-based materials mayalso be utilized. Foam materials have the advantage of having muchgreater strain capacities than neat resin materials. However, it will beappreciated that foam materials have less stiffness than solidmaterials. The Poisson's ratio of the neat resin may be around 0.4 to0.5. This will result in significant lateral expansion and contractionof the foam material 12 with change of wingspan, unless some force isapplied to hold the shape memory polymer material at the desired outermold line. The Poisson's ratio of the shape memory polymer foam may beless than 0.1.

It will be appreciated that the electromagnetic field system 58 may beused to effect shape change in the material 52. Also, an electromagneticfield system as described above may be used in conjunction with othertypes of material, such as superelastic metal foam materials.

FIG. 8 shows an alternative spring arrangement in which a firstconcentric coiled spring pair 80 is located within a shape-changingmaterial 14 at a leading edge 84 of a wing. A second concentric springpair 90 is located within the material 14 at a trailing edge 94 of thewing 10. The spring pairs 80 and 90 are located outside of the skeleton30, and are coiled such that their axes are directed perpendicular tothe plane shown in FIG. 8. One or both of the springs in each springpair 80 and 90 may include a shape memory alloy material. The springpairs 80 and 90 are advantageously located where structural support ismost needed on the wing 10. The spring pairs may thus be more efficientin providing uniform structural support. In addition, the smaller springassemblies 80 and 90 may advantageously provide better, more uniformheating when the spring pairs 80 and 90 are used as resistive heaters.

FIG. 9 shows another spring configuration for the wing 10, with a numberconcentric coil springs or spring pairs 100, 102, 104, 106, and 108 atvarious locations within the shape-changing material 14, outside of theskeleton 30. The spring pairs 100-108 are all linked by a sheet metalconnector 110. The sheet metal connector 110 may be one of multiplesupports at various longitudinal (axial) locations along lengths of thespring pairs 100-108. The sheet metal connector 110, which may be madeof sheet steel or another suitable metal, provides structural supportwing 10, keeping the springs 100-108 in a fixed position relative to oneanother. The sheet metal connector 110 may serve as an alternativestructure to be used in place of the ribs 32 (FIG. 1).

The springs or spring pairs 100-108 may include springs with shapememory alloy materials. Alternatively, the springs 100-108 may all besingle-metal conventional springs.

The above descriptions have related to a single type of structure, anexpandable wing 10. It will be appreciated that the concepts describedherein are applicable to a variety of other structures where shapechange and/or reconfiguration is desired.

Although the invention has been shown and described with respect to acertain preferred embodiment or embodiments, it is obvious thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described elements (components, assemblies,devices, compositions, etc.), the terms (including a reference to a“means”) used to describe such elements are intended to correspond,unless otherwise indicated, to any element which performs the specifiedfunction of the described element (i.e., that is functionallyequivalent), even though not structurally equivalent to the disclosedstructure which performs the function in the herein illustratedexemplary embodiment or embodiments of the invention. In addition, whilea particular feature of the invention may have been described above withrespect to only one or more of several illustrated embodiments, suchfeature may be combined with one or more other features of the otherembodiments, as may be desired and advantageous for any given orparticular application.

1. A shape-changing structural member comprising: a shape-changingstructural material capable of elastic deformation at strains of atleast 5%; and one or more springs embedded in the shape-changingstructural material, wherein the one or more springs provide structuralsupport to the shape-changing material.
 2. The structural member ofclaim 1, wherein the structural material is substantially continuousthroughout the structural member.
 3. The structural member of claim 1,wherein the structural material is a solid polymer material.
 4. Thestructural member of claim 1, wherein the structural material is a foammaterial.
 5. The structural member of claim 4, wherein the foam materialis a polymer foam.
 6. The structural member of claim 5, wherein thepolymer foam is a shape memory polymer foam.
 7. The structural member ofclaim 4, wherein the foam material is a superelastic metal foam.
 8. Thestructural member of claim 7, wherein the superelastic metal foamincludes a metal alloy.
 9. The structural member of claim 1, wherein thefoam material is capable of elastic deformation at strains of at least300%.
 10. The structural member of claim 1, wherein the one or moresprings includes a coil spring.
 11. The structural member of claim 10,wherein an axial length of the one or more springs is in a direction inwhich the shape-changing material is to be extended and retracted. 12.The structural member of claim 1, wherein the one or more springsincludes a pair of coil springs.
 13. The structural member of claim 12,wherein at least one of the coil springs is made of a shape memory metalalloy.
 14. The structural member of claim 12, wherein both of the coilsprings are made of a shape memory metal alloy.
 15. The structuralmember of claim 14, wherein the coil springs have different shape memorytransition temperatures.
 16. The structural member of claim 12, whereinthe coil springs are concentric, with one of the springs inside theother of the springs.
 17. The structural member of claim 16, furthercomprising additional pairs of concentric coil springs; wherein thepairs of coil springs support the shape-changing structural material atdifferent locations within the material.
 18. The structural member ofclaim 17, wherein the pairs of concentric coils springs are connected toeach other by a metal connector.
 19. The structural member of claim 1,wherein the structure is an extendible wing.
 20. An extendible aircraftwing comprising: a shape-changing material configured to be extended andretracted; and a pair of concentric springs embedded in theshape-changing material; wherein the springs have an axial length in adirection in which the shape-changing material is to be extended andretracted; and wherein the springs provide structural support to theshape-changing material.